This invention relates to apparatus for rock cutting and drilling and more particularly relates to mining, tunneling, or drilling machinery comprised of abrasive compact cutters.
A cluster compact is defined as a cluster of abrasive particles bonded together either (1) in a self-bonded relationship, (2) a means of a bonding medium disposed between the crystals, (3) by means of some combination of (1) and (2). Reference can be made to U.S. Pat. Nos. 3,136,615; 3,233,988; and 3,609,818 for a detailed disclosures of certain types of cluster compacts and methods for making same. (The disclosures of these patents are hereby incorporated by reference herein).
A composite compact is defined as a cluster compact bonded to a substrate material such as cemented tungsten carbide. The bond to the substrate can be formed either during or subsequent to the formation of the cluster compact. It is, however, highly preferred to form the bond during formation of the cluster compact. Reference can be made to U.S. Pat. Nos. 3,743,489, 3,745,623 and 3,767,371 for a detailed disclosure of certain types of composite compacts and methods for making same. (The disclosures of these patents are hereby incorporated by reference herein.)
Conventional rotary drill bits for oil and gas well drilling core drilling have heretofore used cutting elements such as (1)steel teeth, (2) steel teeth laminated with tungsten carbide, (3) a compact insert of cemented tungsten carbide, and (4) natural diamonds all of which are set or molded in a tungsten carbide crown or cone. Due to the relatively short life and/or high operating cost of these conventional designs, it has recently been proposed to use synthetic diamond compacts as the cutting element in such drills.
In one prior art design, a drill bit cutting element is formed by attaching a diamond composite compact with a cemented carbide substrate by brazing the carbide substrate to a cemented carbide pin. The pin is mounted in a hole in the drill crown. The diamond layer is generally oriented in a radial sense to the center of rotation of the drill bit and penetrates the rock essentially as a cutting tool in a similar manner to a cutting tool which is used to cut metal on a lathe.
In a second prior art design, a cutting element is formed by furnace brazing a diamond composite compact in a recess of the crown of the drill bit. A portion of the compact is extended beyond the outer surface of the crown and forms a cutting edge for the drill.
One problem which has been encountered in field tests of these designs is that the stresses on each cutting element is severe and some breakage or disattachment of the cutters has been encountered. The stresses are caused because the structure of most rocks is heterogeneous and thus have layers of varying hardness. These layers cause a large variation in the impact loads to be applied to the cutting elements during drilling, and thus, the bond strength of such designs is not always strong enough to withstand such a widely varying impact loading.
The failure of the compact cutters has given rise to a need for the individual repair of the cutters. Heretofore, this has not been practical because in all of the foregoing prior art designs the cutters are permanently mounted in the drill crowns by interference fitting, by molding of the cutters in the crown, or by furnace brazing of the cutters in the crown after formation of the drill crown.
Another problem encountered with such designs is that they do not permit the cutters to be adjusted in height relative to the crown and relative to other cutters after initial mounting of the cutters. This has lead to the premature failure of some cutters due to disproportionate engagement of the compact with the workpiece.
Still other problems are encountered with the prior art assembly techniques. As an example, one furnace brazing technique used with a cutter comprised of a composite compact bonded to a carbide pin is to mold the pin in place during formation of the crown and then simultaneously furnace braze a composite compact to each pin. Difficulty arises in providing adequate quality control for the attachment of the compact to the pin because to rebond one or more compacts, the whole bit must be resubjected to a furnace brazing cycle. This may be detrimental to the bond between the other compacts and pins as well as to the integrity of the abrasive layer which can only withstand limited exposure to the temperatures required to form the bonds.
Accordingly, it is an object of the invention to provide an improved apparatus for rock cutting and drilling.
It is another object of the invention to provide a drill bit comprised of compact cutters, the height of which are adjustable.
It is another object of the invention to provide a drill bit comprised of compact cutters which are removable for repair.
It is another object of the invention to provide a drill bit comprised of compact cutters which can be completely prefabricated prior to attachment to the drill bit crown.